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Developer Guide for PowerModelsDistribution

In this guide we aim to communicate the various code standards expected for PowerModelsDistribution

Documentation

Documentation should be included for all new publicly exported additions to the code base

  • All new formulation should have their hierarchies be documented in /docs/src/formulations.md
  • All new formulations should be summarized in /docs/src/formulation-details.md
  • Additions to the ENGINEERING data model should be added to /docs/src/eng-data-model.md
  • All new constraints should have their mathematical form in their associated docstring
  • The usage details for all new exported functions should be documented via an associated docstring, with the exception of constraint and variable creation functions, which should contain mathematical details in their docstring
  • Summaries of the purpose of new unexported functions should be documented via an associated docstring

Examples

In the case of new functionality, like helper functions for data manipulation or model debugging, or changes to building or running models, Jupyter notebooks should be utilized to demonstrate these features, and are required to exist in the /examples directory.

Style Conventions

In general, the following conventions should be adhered to when making changes or additions to the code base. These conventions should include any conventions applied across the InfrastructureModels ecosystem specific to power engineering (i.e conventions from InfrastructureModels, PowerModels, PowerModelsRestoration, etc.) with some additions specific to PowerModelsDistribution.

Functions

Function additions should meeting the following criteria:

  • All functions should be clearly named, without abbreviations, and with underscores between words, e.g. parse_file or constraint_bus_voltage_magnitude; in Python this is known as lower_case_with_underscores. The exception to the abbreviate rule is cases where abbreviations would be expected in the modeling of power systems.
  • All functions that are not prepended by an underscore _ will be exported by default (i.e. when a user uses using PowerModelsDistribution). Public functions should have a detailed docstring instructing on usage
  • All functions that modify data in place should end with an exclamation point ! and the function input that is being modified should be the first argument (or first arguments in the case where multiple inputs are being modified in place). The exceptions to this rule are constraint and variable creation functions (i.e. those functions related to JuMP model creation), which do not include the exclamation point
  • All function arguments, including keyword arguments, should have their types specified.
  • Private functions, i.e. those intended to be for internal use only, should follow the same descriptive naming conventions as functions exported by default, and should always include docstrings to describe their purpose.
  • Functions should be separated by two blank lines
"this function demonstrates how an internal, in-place data altering function should be defined"
function _concise_descriptive_name!(data::Dict{String,<:Any}, a::Real, b::Vector{<:Real}, c::Matrix{<:Complex}; d::Bool=false, e::Vector{<:Function}=Function[])
end

Types & Enums

When specifying types, i.e. when specifying the type of a function argument, or creating enums, these guidelines are recommended:

  • Prefer to use Vector{T} instead of Array{T,1}
  • Prefer to use Matrix{T} instead of Array{T,2}
  • Enums should only be used in the ENGINEERING data model, never the MATHEMATICAL data model
  • Enums must be added to the JSON parser when introduced

Constants

Whenever possible, const should be used to eliminate unnecessary re-evaluations of code, and every const should have a docstring, whether internal or public.

JuMP Variables and Constraints

For functions that create JuMP variables and constraints in particular, we follow the following naming convention as originally adopted by PowerModels:

<jump macro id>(_<phase variant>)_<comp short name>_<quantity name>(_real|_imaginary|_magnitude|_angle|_factor)(_fr|_to)(_sqr)(_on_off)

in the interest of intuitive names for users, the following special cases are also acceptable,

  • _power_real -(can be replaced with)-> _active
  • _power_imaginary -(can be replaced with)-> _reactive

In the case of PowerModelsDistribution, there are additional tags indicating that a function is a multiconductor variant, three-phase specific, etc.:

  • mc multi-conductor, with an explicit neutral (which is the last conductor by convention?)
  • mp multi-phase, for constraints that have no (explicit) neutral and multiple phases
  • 3p three-phase, when a constraint is hard-coded for three phases

Currently, all phase-aware functions use mc, but this is subject to change in the future as we refactor. If the function is not multiphase specific, these are not needed in the function name.

Formulations

  • All new formulations should have clear error messages when they do not support existing components. For example, if a formulation addition which is intended to work with OPF does not support delta-wye transformers, the constraint_mc_transformer_power_dy
  • Formulation abstract type and mutable struct must be specified in CapitalizedWords, which is a subtype of camelCase with the first word also capitalized.

Problem Specifications

  • If a new problem specification is only needed due to the requirements of a new formulation, and is not a new type of problem, e.g. another OPF formulation, a build_ function with the same name as the existing formulation should be created that accepts a specific PowerModel (multiple dispatch)
  • If a new problem specification is a new type of problem that will e.g. accept multiple formulations, new build_ and run_ functions should be created that do not collide with existing problem specification functions

Metaprogramming

In general, it is better to avoid metaprogramming patterns, like creating functions algorithmically, in order to aid in the debugging of code. Metaprogramming can create significant challenges in interpreting stacktraces upon errors.

Markdown

Markdown files should be properly formatted, particularly when including tables. Developers are encouraged to use markdownlint and a markdown formatter (such as in VSCode).

File Structure

It is important that new functions, variables, constraints, etc. all go into appropriate places in the code base so that future maintenance and debugging is easier. Pay attention to the current file structure and attempt to conform as best as possible to it. In general

  • /src/core contains the core logic of the package, including variable creation and constraint templates, i.e. things that are agnostic to the formulation
  • /src/data_model contains all of the logic to transform between the ENGINEERING and MATHEMATICAL data models and model creation helper tools
  • src/form contains formulation specific variable and constraint functions, organized under separate files for different formulations
  • src/io contains all of the tools to parse and save files, in particular all of the logic necessary to parse dss files and output json files
  • src/prob contains all problem specifications
  • docs/src contains all source markdown files for the documentation
  • examples contains Jupyter notebooks with walkthroughs of PowerModelsDistribution for new users

Dependencies (Project.toml)

All new dependencies should be carefully considered before being added. It is important to keep the number of external dependencies low to avoid reliance on features that may not be maintained in the future. If possible, Julia Standard Library should be used, particularly in the case where reproducing the desired feature is trivial. There will be cases where it is not simple to duplicate a feature and subsequently maintain it within the package, so adding a dependency would be appropriate in such cases.

All new dependencies are are ultimately approved should also include an entry under [compat] indicating the acceptable versions (Julia automerge requirement). This includes test-only dependencies that appear under [extras]

The Manifest.toml should not be included in the repo.

Pull Requests

All pull requests should be reviewed by a core developer, and may include a review by a subject matter expert if the area of the PR is outside that of one of the core developers. In that case, the core developers will primarily review style and design, rather than substance.

Every PR to PowerModelsDistribution should strive to meet the following guidelines.

PR Title

  • Should be concise and clear, describing in a phrase the content of the PR
  • Should include a prefix that describes the primary type of the PR
    • ADD: feature addition
    • FIX: bugfix
    • REF: refactor
    • UPD: updates to code for e.g. version bumps of dependencies
    • STY: style changes, no changes to function names, added features, etc.
    • DOC: documentation-only additions/changes
    • RM: dead code removal

PR Body

  • If the change is breaking, it should be clearly stated up front
  • The purpose of this PR should be clearly stated right away
  • Major changes / additions to the code should be summarized. In the case where a refactor was performed, the name changes of public functions should be documented in the body of the PR
  • Any associated Issues should be referenced in the body of the PR, and it is accepted/encouraged to use Closes #XX to automatically close Issues after the PR is merged

PR Code

  • An entry should be added to CHANGELOG.md for every PR
  • Documentation should be updated (See Documentation section above for guidelines)
  • Unit tests should be added. In the case where existing unit tests were altered, an explanation for the change must be included
  • Code should be rebased to the latest version of whatever branch the PR is aimed at (no merge conflicts!)

Versions

PowerModelsDistribution follows the Semantic Versioning (SemVer) convention of Major.minor.patch, where Major indicates breaking changes, minor indicates non-breaking feature additions, and patch indicates non-breaking bugfixes.

Currently, because Major==0, minor indicates breaking changes and patch indicates any non-breaking change, including both feature additions and bugfixes. Once PowerModelsDistribution reaches v1.0.0, we will adhere strictly to the SemVer convention.

Branch Management

The main branch is a protected branch, meaning that its history will always be contiguous and can never be overwritten.

Release candidate branches of the format vM.m.0-rc are also protected branches. These branches will contain only breaking changes and will not be merged into main until a new version is ready to be tagged. Pull requests including breaking changes should be directed into the next release candidate branch available, e.g. if the current version of the package is v0.9.0, the next release candidate branch will be v0.10.0-rc.

Pull requests that include only non-breaking changes can be merged directly into main once approved, and in the case of merge conflicts arising for release candidate branches, the -rc branch will need to be updated to include the latest main.

Pull requests will generally be merged using squash and merge into the branch they are aimed at, with the exception of release candidate branches, which generally be merged using rebase and merge into main.